1. Field of the Invention
Quality monitoring of a data transmission circuit requires, first, the identification and record of errors in the digital signal or the failure of the signal, and, second, the identification of long-term changes in the transmission properties of the transmission circuits. The invention accomplishes this.
2. Description of the Prior Art
The structure of a centrally controlled emergency switching system is known from the periodical "Telcom Report" of 10 (1987) No. 2, pages 102 through 108, FIG. 8. Transmission circuits have switching stations that are also referred to as digital signal distributors or as cross-connect equipment, these are connected to regional centers which are located in communication with a network management center. When, for example, a regional center reports an interruption of the transmission circuit, then the network management circuit initiates the switching of a standby route.
A synchronous digital signal hierarchy is known from the publication CCITT Draft Recommendations G.70X, G.70Y and G.70Z. Digital signals of the lowest hierarchy level comprise a bit rate of 155.52 Mbit/s and a pulse frame which is referred to as a synchronous transport module STM-1. This is composed of a section overhead, an administration unit and an administration unit pointer. A virtual container which starts to indicate the administration unit pointer can be inserted into the administration unit. The virtual container is in turn composed of a path overhead and of a container in which a 139.264 Mbit/s signal exists. See also British patent No. 1,401,261, German No. 2,556,079, and the publication "International Telegraph and Telephone Consultative Committee Period 1985-1988 COM XVIII-113-E November 1987, Title Report of The Meetings of Experts on Broadband Interface Aspects of Study Group XVIII (Geneva, 9-11 November 1987) pages 1-87.